1. Field of the Invention
The present invention relates to a polymer gel electrolyte composition and a method of producing the same. More specifically, the present invention relates to a polymer gel electrolyte composition constituted by a crosslinked polymer network matrix of a three-dimensional crosslinked structure, which contains an electrolyte solution, and a non-crosslinked polymer contained in the matrix, and a method of producing the same.
2. Description of the Related Art
Electrochemical devices such as lithium ion secondary batteries, electrochromic devices, wet photovoltaic cells, capacitors, electric double-layer capacitors and sensors require an electrolyte to make them function. However, when the electrolyte is liquid, the electrolyte liquid must be sealed tightly to prevent troubles due to leakage of the liquid or short-circuiting, or requires a strong casing to prevent accidents due to shock, making it very difficult to reduce the weight or thickness of the electrochemical device. Then, there have been a number of attempts made to solidify the electrolyte solution. For example, an all-solid state type polymer battery using a solid electrolyte has been proposed (See, for example, Electrochimica Acta, 40 (13-14), 2177, 1995.) However, using solid electrolytes, it is difficult to obtain a device that has a practical performance at room temperature or less because of the poor ion conductivity of the solid-state materials.
Then, a battery that uses a so-called gel-type polymer electrolyte, which can prevent the leakage of the electrolyte solution and improve the ion conductivity, by using a gel obtained by swelling a polymer film with an electrolyte solution, has been developed and is widely used in cell phones, personal computers, etc. (See, for example, U.S. Pat. No. 5,418,091, and “Electrochemistry” 53(8), 619 (1985).) Up to now, as such a gel-type polymer electrolyte, a polymer gel electrolyte prepared using a polyacrylonitrile (PAN)-based polymer (Jpn. Pat. Appln. KOKAI Publication No. 4-306506 and Jpn. Pat. Appln. KOKAI Publication No. 7-54271), a polyethylene oxide (PEO)-based polymer (Jpn. Pat. Appln. KOKAI Publication No. 62-285954 and Jpn. Pat. Appln. KOKAI Publication No. 6-68906), or a polymethyl methacrylate (PMMA)-based polymer has been mainly developed. Further, it has been proposed that a polyvinylidene fluoride (PVDF) film is utilized for the gel electrolyte (See, for example, U.S. Pat. No. 5,418,091).
However, all of these polymer gel electrolytes are still not satisfactory in terms of heat resisting property and ion conductivity. Further, those which contain a large amount of halogen element, such as PVDF, may raise an environmental problem caused by generation of hydrogen fluoride or the like when the battery is disposed of by incineration.
In order to increase the energy density of the battery, for example, a thinner and smaller battery needs to be developed. In such a case, it is essential to develop a novel high-performance material that can achieve this object, and a new technology that can efficiently produce the material. For example, in order to charge and discharge a battery at a high speed, it is necessary to have a film-shaped gel electrolyte that has a high ion conductivity and that can be processed thinner. Further, in order to prevent leakage of the electrolyte solution, it is essential to have a high heat-resistant gel film that is not liquefied but is able to maintain its shape even at a high temperature. Furthermore, in light-related devices, it is essential that the electrolytic film have a transparency.
Thus, an object of the present invention is to provide a polymer gel electrolyte composition having a high ion conductivity, an excellent thermostability and a transparency, and a method of producing such a composition.